Heat treatment susceptor and heat treatment apparatus

ABSTRACT

A plurality of substrate support pins are provided upright on a holding plate so as to contact a position on which no stress is exerted in a lower surface of a semiconductor wafer when an upper surface of the semiconductor wafer is irradiated with flash light emitted from a flash lamp and thus reaches a maximum temperature. When the application of the flash light causes the upper surface of the semiconductor wafer to warp such that the upper surface becomes raised, stress concentration does not occur in the contact position of the lower surface of the semiconductor wafer that contacts the plurality of substrate support pins. The semiconductor wafer can be prevented from breaking during the application of the flash light.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of prior U.S. patent applicationSer. No. 15/382,828, filed Dec. 19, 2016, by Kazuhiko FUSE, entitled“HEAT TREATMENT SUSCEPTOR AND HEAT TREATMENT APPARATUS,” which claimspriority to Japanese Patent Application No. JP2016-018849, filed Feb. 3,2016. The entire contents of each of these patent applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a heat treatment susceptor that holds athin-plate precision electronic substrate (hereinafter, merely referredto as a “substrate”), such as a semiconductor wafer, that is irradiatedwith flash light emitted from a flash lamp for heat treatment of thesubstrate, and relates to a heat treatment apparatus that includes theheat treatment susceptor.

Description of Background Art

In the process of manufacturing a semiconductor device, the introductionof impurities is an essential step for forming pn junctions in asemiconductor wafer. At present, it is common to introduce impurities byion implantation and subsequent annealing. Ion implantation is atechnique for physically implanting impurities by causing impurityelements such as boron (B), arsenic (As), and phosphorus (P) to beionized and collide with a semiconductor wafer with a high accelerationvoltage. The implanted impurities are activated by annealing. If, atthis time, annealing time is approximately several seconds or longer,the implanted impurities are deeply diffused by heat. As a result, ajunction depth may become deeper than necessary, possibly interferingwith the formation of an excellent device.

For this reason, flash-lamp annealing (FLA) has recently been receivingattention as an annealing technique for heating a semiconductor wafer inan extremely short time. Flash-lamp annealing is a heat treatmenttechnique using xenon flash lamps (hereinafter, “flash lamps” simplyreferred to indicate xenon flash lamps) to irradiate the surface of asemiconductor wafer with flash light such that the temperature of onlythe surface of the semiconductor wafer that is implanted with impuritiesis raised in an extremely short time (several milliseconds or less).

The xenon flash lamps have a spectral distribution of radiation rangingfrom ultraviolet regions to near-infrared regions. The wavelength oflight emitted from the xenon flash lamps is shorter than that of lightemitted from conventional halogen lamps and substantially coincides withthe fundamental absorption band of a silicon semiconductor wafer. Thus,the temperature of the semiconductor wafer can be rapidly increased witha small amount of transmitted light when the semiconductor wafer isirradiated with flash light from the xenon flash lamps. It has also beendetermined that the irradiation with flash light in an extremely shorttime of several milliseconds or less can selectively raise thetemperature of only the vicinity of the surface of the semiconductorwafer. Accordingly, such a temperature rise in an extremely short timeusing the xenon flash lamps allows the impurities to be only activatedwithout being deeply diffused.

As examples of typical heat treatment apparatuses with flash lamps, US2009/0175605 and US 2014/0235072, for example, disclose heat treatmentapparatuses that include flash lamps emitting flash light to asemiconductor wafer supported by a plurality of support pins providedupright on a susceptor.

However, since the flash lamps instantaneously emit the flash lighthaving extremely high energy to the front surface of the semiconductorwafer, the temperature of the front surface of the semiconductor waferinstantaneously rapidly increases while the temperature of the backsurface does not increase so much. Thus, abrupt thermal expansionoccurring only in the front surface of the semiconductor wafer causesdeformation in the semiconductor wafer such that the front surface warpsand becomes raised. As a result, stress concentration in the backsurface of the semiconductor wafer causes the semiconductor wafer tobreak.

SUMMARY OF THE INVENTION

The present invention is directed to a heat treatment susceptor thatholds a substrate irradiated with flash light emitted from a flash lampfor heat treatment of the substrate.

In an aspect of the present invention, the heat treatment susceptorincludes: a holding plate having a planar holding surface; and aplurality of support pins that are provided upright on the holdingsurface and contact a lower surface of the substrate at upper ends tosupport the substrate. The plurality of support pins are providedupright so as to contact a position on which no stress is exerted in thelower surface of the substrate when an upper surface of the substrate isirradiated with flash light emitted from the flash lamp and thus reachesa maximum temperature.

Stress concentration does not occur in the contact position of the lowersurface of the substrate that contacts the support pins during theapplication of the flash light. This can prevent the substrate frombreaking during the application of the flash light emitted from theflash lamp.

The present invention is also directed to a heat treatment apparatusthat heats the substrate by applying flash light to the substrate.

In an aspect of the present invention, the heat treatment apparatusincludes: a chamber that houses a substrate; the heat treatmentsusceptor according to claim 1; and a flash lamp that applies flashlight to the substrate held by the heat treatment susceptor.

The substrate heat-treated by the application of the flash light in theheat treatment apparatus can be prevented from breaking.

The present invention therefore has an object to prevent the substratefrom breaking during the application of the flash light from the flashlamp.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing a configuration ofa heat treatment apparatus according to the present invention;

FIG. 2 is a perspective view showing an overall external view of aholder;

FIG. 3 is a plan view of a susceptor;

FIG. 4 is a cross-sectional view of the susceptor;

FIG. 5 is a plan view of a transfer mechanism;

FIG. 6 is a side view of the transfer mechanism;

FIG. 7 is a plan view showing arrangement of a plurality of halogenlamps;

FIG. 8 is a schematic view showing how a semiconductor wafer warpsduring application of flash light;

FIG. 9 shows a transition of a position on which no stress is exerted ina lower surface of the semiconductor wafer during the application of theflash light; and

FIG. 10 shows a stress distribution of the lower surface of thesemiconductor wafer during the application of the flash light.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a preferred embodiment of the present invention will bedescribed in detail with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view showing a configuration ofa heat treatment apparatus 1 according to the present invention. Theheat treatment apparatus 1 in this preferred embodiment is a flash-lampannealing apparatus that heats a disc-shaped semiconductor wafer Wserving as a substrate by applying flash light to the semiconductorwafer W. Although the size of the semiconductor wafer W to be treated isnot particularly limited, the semiconductor wafer W may have a diameterof, for example, 300 mm or 450 mm. The semiconductor wafer W isimplanted with impurities before being transported into the heattreatment apparatus 1, and the implanted impurities are activatedthrough heat treatment by the heat treatment apparatus 1. To facilitatethe understanding, the dimensions and number of each part areexaggerated or simplified as necessary in FIG. 1 and subsequentdrawings.

The heat treatment apparatus 1 includes a chamber 6 that houses thesemiconductor wafer W, a flash heater 5 with a plurality of built-inflash lamps FL, and a halogen heater 4 with a plurality of built-inhalogen lamps HL. The flash heater 5 is provided above the chamber 6,and the halogen heater 4 is provided below the chamber 6. The heattreatment apparatus 1 also includes, within the chamber 6, a holder 7that holds the semiconductor wafer W in a horizontal position, and atransfer mechanism 10 that transfers the semiconductor wafer W betweenthe holder 7 and the outside of the apparatus. The heat treatmentapparatus 1 further includes a controller 3 that controls operatingmechanisms located in the halogen heater 4, the flash heater 5, and thechamber 6 for heat treatment of the semiconductor wafer W.

The chamber 6 is formed of a tubular chamber side portion 61 and quartzchamber windows attached to the top and bottom of the chamber sideportion 61. The chamber side portion 61 has a substantially tubularshape that is open at the top and bottom, the opening at the top beingequipped with and closed by an upper chamber window 63, the opening atthe bottom being equipped with and closed by a lower chamber window 64.The upper chamber window 63, which forms the ceiling portion of thechamber 6, is a disc-shaped member made of quartz and functions as aquartz window that allows flash light emitted from the flash heater 5 topass through into the chamber 6. The lower chamber window 64, whichforms the floor portion of the chamber 6, is also a disc-shaped membermade of quartz and functions as a quartz window that allows lightemitted from the halogen heater 4 to pass through into the chamber 6.

A reflection ring 68 is mounted on the upper portion of the inner wallsurface of the chamber side portion 61, and a reflection ring 69 ismounted on the lower portion thereof. Both of the reflection rings 68and 69 have an annular shape. The upper reflection ring 68 is mounted bybeing fitted from above the chamber side portion 61. On the other hand,the lower reflection ring 69 is mounted by being fitted from below thechamber side portion 61 and fastened with screws (not shown). In otherwords, the reflection rings 68 and 69 are both removably mounted on thechamber side portion 61. The chamber 6 has an inner space that issurrounded by the upper chamber window 63, the lower chamber window 64,the chamber side portion 61, and the reflection rings 68 and 69 and thatis defined as a heat treatment space 65.

With the reflection rings 68 and 69 mounted on the chamber side portion61, the chamber 6 has a recessed portion 62 in its inner wall surface.In other words, the recessed portion 62 is formed by being surrounded bya central portion of the inner wall surface of the chamber side portion61 on which the reflection rings 68 and 69 are not mounted, a lower endface of the reflection ring 68, and an upper end face of the reflectionring 69. The recessed portion 62 is horizontally formed in an annularshape in the inner wall surface of the chamber 6 and surrounds theholder 7 that holds the semiconductor wafer W.

The chamber side portion 61 and the reflection rings 68 and 69 are eachmade of a metal material (e.g., stainless steel) having excellentstrength and excellent heat resistance. The inner circumferentialsurfaces of the reflection rings 68 and 69 are mirror-finished byelectrolytic nickel plating.

The chamber side portion 61 has a transport opening (throat) 66 throughwhich the semiconductor wafer W is transported into and out of thechamber 6. The transport opening 66 is openable and closeable with agate valve 185. The transport opening 66 is communicatively connected tothe outer circumferential surface of the recessed portion 62. Whenopened by the gate valve 185, the transport opening 66 allows thesemiconductor wafer W to be transported into and out of the heattreatment space 65 from the transport opening 66 through the recessedportion 62. When the transport opening 66 is closed by the gate valve185, the heat treatment space 65 in the chamber 6 becomes an enclosedspace.

The chamber 6 has, in its upper portion of the inner wall, a gas supplyport 81 through which a treatment gas (in the present embodiment,nitrogen gas (N₂)) is supplied to the heat treatment space 65. The gassupply port 81 is formed at a position above the recessed portion 62 andmay be formed in the reflection ring 68. The gas supply port 81 iscommunicatively connected to a gas supply pipe 83 via a buffer space 82formed in an annular shape inside the side wall of the chamber 6. Thegas supply pipe 83 is connected to a gas supply source 85. A valve 84 isinterposed in the path of the gas supply pipe 83. When the valve 84 isopened, the nitrogen gas is supplied from the gas supply source 85 intothe buffer space 82. The nitrogen gas flowing into the buffer space 82spreads out in the buffer space 82, which has lower fluid resistancethan that of the gas supply port 81, and is then supplied through thegas supply port 81 into the heat treatment space 65. Note that thetreatment gas is not limited to nitrogen gas, and may be an inert gassuch as argon (Ar) or helium (He) or a reactive gas such as oxygen (O₂),hydrogen (H₂), chlorine (Cl₂), hydrogen chloride (HCl), ozone (O₃), orammonia (NH₃).

The chamber 6 also has, in its lower portion of the inner wall, a gasexhaust port 86 through which the gas in the heat treatment space 65 isexhausted. The gas exhaust port 86 is formed at a position below therecessed portion 62 and may be formed in the reflection ring 69. The gasexhaust port 86 is communicatively connected to a gas exhaust pipe 88via a buffer space 87 formed in an annular shape inside the side wall ofthe chamber 6. The gas exhaust pipe 88 is connected to an exhaust part190. A valve 89 is interposed in the path of the gas exhaust pipe 88.When the valve 89 is opened, the gas in the heat treatment space 65 isdischarged from the gas exhaust port 86 through the buffer space 87 intothe gas exhaust pipe 88. A configuration is also possible in which aplurality of gas supply ports 81 and a plurality of gas exhaust ports 86are provided along the circumference of the chamber 6 or in which thegas supply port 81 and the gas exhaust port 86 have slit shapes. The gassupply source 85 and the exhaust part 190 may be mechanisms provided inthe heat treatment apparatus 1, or they may be utilities in a factorywhere the heat treatment apparatus 1 is installed.

One end of the transport opening 66 is also connected to a gas exhaustpipe 191 through which the gas in the heat treatment space 65 isdischarged. The gas exhaust pipe 191 is connected to the exhaust part190 via a valve 192. When the valve 192 is opened, the gas in thechamber 6 is discharged through the transport opening 66.

FIG. 2 is a perspective view showing an overall external view of theholder 7. The holder 7 includes a base ring 71, connecting parts 72, anda susceptor 74. The base ring 71, the connecting parts 72, and thesusceptor 74 are all made of quartz. In other words, the entire holder 7is made of quartz.

The base ring 71 is a quartz member having an arc shape that is anannular shape with a missing part. The missing part is formed to preventinterference between transfer arms 11 of the transfer mechanism 10,which will be described below, and the base ring 71. The base ring 71 isplaced on the bottom surface of the recessed portion 62 and thussupported on the wall surface of the chamber 6 (see FIG. 1 ). On theupper surface of the base ring 71, a plurality of (in the presentembodiment, four) connecting parts 72 are provided upright along thecircumference of the base ring 71. The connecting parts 72 are alsoquartz members and are fixedly attached to the base ring 71 by welding.

The susceptor 74 is supported by the four connecting parts 72 providedon the base ring 71. FIG. 3 is a plan view of the susceptor 74. FIG. 4is a cross-sectional view of the susceptor 74. The susceptor 74 includesa holding plate 75, a guide ring 76, and a plurality of substratesupport pins 77. The holding plate 75 is a substantially circular flatplate-like member made of quartz. The holding plate 75 has a diametergreater than that of the semiconductor wafer W. In other words, theholding plate 75 has a plane size greater than that of the semiconductorwafer W.

The guide ring 76 is installed on the peripheral portion of the uppersurface of the holding plate 75. The guide ring 76 is an annular shapedmember having an inside diameter greater than the diameter of thesemiconductor wafer W. For example, when the semiconductor wafer W has adiameter of 300 mm, the guide ring 76 has an inside diameter of 320 mm.The inner circumference of the guide ring 76 is a tapered surface thattapers from above down to the holding plate 75. The guide ring 76 ismade of the same quartz as that of the holding plate 75. The guide ring76 may be welded to the upper surface of the holding plate 75, or may befixed to the holding plate 75 with pins that are separately processed,for example. Alternatively, the holding plate 75 and the guide ring 76may be processed as an integral member.

Of the upper surface of the holding plate 75, a region located closer tothe inside than the guide ring 76 serves as a planar holding surface 75a on which the semiconductor wafer W is held. The plurality of substratesupport pins 77 are provided upright on the holding surface 75 a of theholding plate 75. In this preferred embodiment, a total of 12 substratesupport pins 77 are provided upright every 30 degrees along thecircumference of a circle concentric with the outer circumferentialcircle of the holding surface 75 a (the inner circumferential circle ofthe guide ring 76). The diameter (the distance between opposed substratesupport pins 77) of the circle along which the 12 substrate support pins77 are disposed is smaller than the diameter of the semiconductor waferW, and is 270 mm when the semiconductor wafer W has a diameter of 300mm. All the substrate support pins 77 are made of quartz. The pluralityof substrate support pins 77 may be provided upright by being welded tothe upper surface of the holding plate 75, or may be processed togetherwith the holding plate 75. The arrangement positions of the substratesupport pins 77 will be further described below in detail.

Referring back to FIG. 2 , the four connecting parts 72 provided uprighton the base ring 71 and the peripheral portion of the holding plate 75of the susceptor 74 are fixedly attached to each other by welding. Inother words, the susceptor 74 and the base ring 71 are fixedly connectedto each other by connecting parts 72. The base ring 71 of the holder 7is supported on the wall surface of the chamber 6, and thus the holder 7is attached to the chamber 6. With the holder 7 attached to the chamber6, the holding plate 75 of the susceptor 74 is in a horizontal position(a position at which the normal coincides with the vertical direction).In other words, the holding surface 75 a of the holding plate 75 is ahorizontal surface.

The semiconductor wafer W transported into the chamber 6 is placed andheld in the horizontal position on the susceptor 74 of the holder 7attached to the chamber 6. At this time, the semiconductor wafer W issupported by the 12 substrate support pins 77 provided upright on theholding plate 75, and is held by the susceptor 74. More specifically,the semiconductor wafer W is supported by upper end portions of the 12substrate support pins 77 in contact with the lower surface of thesemiconductor wafer W. The 12 substrate support pins 77 have the uniformheight (the distance from the upper end of the substrate support pins 77to the holding surface 75 a of the holding plate 75). Thus, the 12substrate support pins 77 can support the semiconductor wafer W in thehorizontal position.

The semiconductor wafer W is supported by the plurality of substratesupport pins 77 with a predetermined gap from the holding surface 75 aof the holding plate 75. The thickness of the guide ring 76 is greaterthan the height of the substrate support pins 77. Thus, the guide ring76 prevents the position of the semiconductor wafer W supported by theplurality of substrate support pins 77 from being shifted in thehorizontal direction.

As shown in FIGS. 2 and 3 , the holding plate 75 of the susceptor 74 hasa vertically penetrating opening 78. The opening 78 is formed to allow aradiation thermometer 120 (see FIG. 1 ) to receive radiation (infraredlight) radiated from the back surface of the semiconductor wafer W heldby the susceptor 74. More specifically, the radiation thermometer 120receives, through the opening 78, the light radiated from the backsurface of the semiconductor wafer W held by the susceptor 74, and thetemperature of the semiconductor wafer W is measured by a separatelyplaced detector. The holding plate 75 of the susceptor 74 further hasfour through holes 79 that lift pins 12 of the transfer mechanism 10,which will be described below, pass through to transfer thesemiconductor wafer W.

FIG. 5 is a plan view of the transfer mechanism 10. FIG. 6 is a sideview of the transfer mechanism 10. The transfer mechanism 10 includestwo transfer arms 11. The transfer arms 11 have an arc shape thatextends substantially along the annular recessed portion 62. Each of thetransfer arms 11 has two upright lift pins 12. Each of the transfer arms11 is pivotable by a horizontal movement mechanism 13. The horizontalmovement mechanism 13 horizontally moves the pair of transfer arms 11between a transfer operation position (position indicated by the solidline in FIG. 5 ) at which the semiconductor wafer W is transferred tothe holder 7 and a retracted position (position indicated by the dasheddouble-dotted line in FIG. 5 ) at which the transfer arms 11 do notoverlap the semiconductor wafer W held by the holder 7 in a plan view.The horizontal movement mechanism 13 may be a mechanism for separatelypivoting the transfer arms 11 by separate motors, or may be a mechanismfor using a link mechanism to pivot the pair of transfer arms 11 inconjunction with each other by a single motor.

The pair of transfer arms 11 are also elevated and lowered together withthe horizontal movement mechanism 13 by an elevating mechanism 14. Whenthe elevating mechanism 14 elevates the pair of transfer arms 11 at thetransfer operation position, a total of four lift pins 12 pass throughthe through holes 79 (see FIGS. 2 and 3 ) formed in the susceptor 74,and the upper ends of the lift pins 12 protrude from the upper surfaceof the susceptor 74. On the other hand, when the elevating mechanism 14lowers the pair of transfer arms 11 at the transfer operation positionto pull the lift pins 12 out of the through holes 79, and the horizontalmovement mechanism 13 moves the pair of transfer arms 11 to open thetransfer arms 11, each of the transfer arms 11 moves to its retractedposition. The retracted position of the pair of transfer arms 11 isdirectly above the base ring 71 of the holder 7. Since the base ring 71is placed on the bottom surface of the recessed portion 62, theretracted position of the transfer arms 11 is inside the recessedportion 62. Note that an exhaust mechanism (not shown) is also providednear the area where the driving parts (the horizontal movement mechanism13 and the elevating mechanism 14) of the transfer mechanism 10 areprovided so that the atmosphere around the driving parts of the transfermechanism 10 is discharged to the outside of the chamber 6.

Referring back to FIG. 1 , the flash heater 5 provided above the chamber6 includes, inside a casing 51, a light source composed of a pluralityof (in the present embodiment, 30) xenon flash lamps FL and a reflector52 provided so as to cover the top of the light source. The casing 51 ofthe flash heater 5 has a lamp-light radiation window 53 attached to thebottom to the casing 51. The lamp-light radiation window 53, which formsthe floor portion of the flash heater 5, is a plate-like quartz windowmade of quartz. Since the flash heater 5 is disposed above the chamber6, the lamp-light radiation window 53 is opposed to the upper chamberwindow 63. The flash lamps FL apply flash light to the heat treatmentspace 65 from above the chamber 6 through the lamp-light radiationwindow 53 and the upper chamber window 63.

The plurality of flash lamps FL are each a rod-shaped lamp having anelongated cylindrical shape and are arranged in a planar array such thattheir longitudinal directions are parallel to one another along the mainsurface of the semiconductor wafer W held by the holder 7 (i.e., in thehorizontal direction). Thus, the plane formed by the array of the flashlamps FL is also a horizontal plane.

The xenon flash lamps FL each include a rod-shape glass tube (dischargetube) and a trigger electrode provided on the outer circumferentialsurface of the glass tube, the glass tube containing xenon gas sealedtherein and including an anode and a cathode that are disposed atopposite ends of the glass tube and connected to a capacitor. Noelectricity flows through the glass tube in a normal state even ifelectric charge is stored in the capacitor because xenon gas is anelectrical insulating material. However, if an electrical breakdown iscaused by application of a high voltage to the trigger electrode, theelectricity stored in the capacitor instantaneously flows through theglass tube, and xenon atoms or molecules are excited at that time tocause light emission. The xenon flash lamps FL have the characteristicsof being able to apply extremely intense light as compared withcontinuous lighting sources such as halogen lamps HL because theelectrostatic energy previously stored in the capacitor is convertedinto an extremely short optical pulse of 0.1 to 100 milliseconds. Inother words, the flash lamps FL are pulsed light-emitting lamps thatinstantaneously emit light in an extremely short time of less than asecond. In addition, light emission time of the flash lamps FL can beadjusted by a coil constant of a lamp power supply that supplies powerto the flash lamps FL.

The reflector 52 is provided above the plurality of flash lamps FL so asto cover all of the flash lamps FL. A basic function of the reflector 52is to reflect the flash light emitted from the plurality of flash lampsFL toward the heat treatment space 65. The reflector 52 is formed of analuminum alloy plate and has a surface (a surface opposed to the flashlamps FL) that is roughened by blasting.

The halogen heater 4 provided below the chamber 6 includes a pluralityof (in the present embodiment, 40) halogen lamps HL inside a casing 41.The halogen heater 4 is a light emitting part that heats thesemiconductor wafer W with the plurality of halogen lamps HL that emitlight from below the chamber 6 through the lower chamber window 64 tothe heat treatment space 65.

FIG. 7 is a plan view showing arrangement of the plurality of halogenlamps HL. 40 halogen lamps HL are divided into two rows so as to bedisposed in an upper row and a lower row. 20 halogen lamps HL aredisposed in the upper row close to the holder 7, and 20 halogen lamps HLare disposed in the lower row farther from the holder 7 than the upperrow. Each of the halogen lamps HL is a rod-shaped lamp having anelongated cylindrical shape. The 20 halogen lamps HL in each of theupper row and the lower row are arranged such that their longitudinaldirections are parallel to one another along the main surface of thesemiconductor wafer W held by the holder 7 (i.e., in the horizontaldirection). Thus, both of the planes formed by the arrays of the halogenlamps HL in the upper and lower rows are horizontal planes.

As shown in FIG. 7 , in each of the upper and lower rows, the halogenlamps HL are disposed at a higher density in a region opposed to theperipheral portion of the semiconductor wafer W held by the holder 7than in a region opposed to the central portion of the semiconductorwafer W. In other words, in both of the upper and lower rows, the pitchof arrangement of the halogen lamps HL in the peripheral portion of thearray of the halogen lamps HL is shorter than that in the centralportion of the array. This allows a larger amount of light to be appliedto the peripheral portion of the semiconductor wafer W where thetemperature tends to drop during heating by the application of lightfrom the halogen heater 4.

A lamp group of the halogen lamps HL in the upper row and a lamp groupof the halogen lamps HL in the lower row are arranged so as to intersecteach other in the grid-like pattern. In other words, a total of 40halogen lamps are disposed such that the longitudinal direction of thehalogen lamps HL in the upper row and the longitudinal direction of thehalogen lamps HL in the lower row are orthogonal to each other.

The halogen lamps HL are filament light sources in which a current isapplied to a filament disposed in the glass tube to make the filamentincandescent and emit light. The glass tube contains a gas sealedtherein, the gas being prepared by introducing a trace amount of halogenelements (such as iodine and bromine) into inert gas such as nitrogenand argon. The introduction of the halogen elements allows thetemperature of the filament to be set to a high temperature whilesuppressing breakage of the filament. Thus, the halogen lamps HL havethe characteristics of lasting longer than typical incandescent lampsand being able to continuously apply intense light. In other words, thehalogen lamps HL are continuous lighting lamps that continuously emitlight for at least one or more seconds. The halogen lamps HL are therod-shaped lamps, thereby lasting long. The halogen lamps HL disposed inthe horizontal direction enhance the efficiency of radiation of thesemiconductor wafer W located above the halogen lamps HL.

The halogen heater 4 also includes a reflector 43 provided below thehalogen lamps HL in the two rows (FIG. 1 ) in the casing 41. Thereflector 43 reflects the light emitted from the plurality of halogenlamps HL toward the heat treatment space 65.

The controller 3 controls the above-described various operatingmechanisms provided in the heat treatment apparatus 1. The controller 3has a similar hardware configuration to that of a commonly usedcomputer. More specifically, the controller 3 includes a CPU that is acircuit for performing various types of computation processing, a ROMthat is a read-only memory for storing basic programs, a RAM that is areadable and writable memory for storing various pieces of information,and a magnetic disk for storing control software and data. Theprocessing in the heat treatment apparatus 1 proceeds by the CPU of thecontroller 3 executing a predetermined processing program.

The heat treatment apparatus 1 includes, in addition to theabove-described components, various cooling structures in order toprevent an excessive temperature increase in the halogen heater 4, theflash heater 5, and the chamber 6 due to heat energy generating from thehalogen lamps HL and the flash lamps FL during the heat treatment of thesemiconductor wafer W. For example, the chamber 6 includes awater-cooled tube (not shown) in the wall. The halogen heater 4 and theflash heater 5 have an air cooling structure for forming a gas flowtherein to exhaust heat. Air is also supplied to a gap between the upperchamber window 63 and the lamp-light radiation window 53 to cool theflash heater 5 and the upper chamber window 63.

Next, a procedure for the treatment of the semiconductor wafer W in theheat treatment apparatus 1 will be described. The semiconductor wafer Wto be treated here is a semiconductor substrate implanted withimpurities (ions) by ion implantation. The impurities are activatedthrough heat treatment (annealing) involving the application of flashlight by the heat treatment apparatus 1. The procedure for the treatmentperformed by the heat treatment apparatus 1 described below isimplemented by the controller 3 controlling each operating mechanism ofthe heat treatment apparatus 1.

First, the valve 84 for supplying a gas and the valves 89, 192 forexhausting a gas are opened to start the supply and discharge of a gasinto and from the chamber 6. When the valve 84 is opened, nitrogen gasis supplied from the gas supply port 81 into the heat treatment space65. When the valve 89 is opened, the gas in the chamber 6 is dischargedfrom the gas exhaust port 86. Accordingly, the nitrogen gas suppliedfrom above the heat treatment space 65 within the chamber 6 flowsdownward and is discharged from below the heat treatment space 65.

The valve 192 is opened to discharge the gas in the chamber 6 also fromthe transport opening 66. The atmosphere around the driving parts of thetransfer mechanism 10 is also discharged from an exhaust mechanism (notshown). During the heat treatment of the semiconductor wafer W in theheat treatment apparatus 1, the nitrogen gas is continuously suppliedinto the heat treatment space 65, and the amount of the nitrogen gassupplied is changed as appropriate in accordance with the processingstep.

Subsequently, the gate valve 185 is opened to open the transport opening66, and the ion-implanted semiconductor wafer W is transported into theheat treatment space 65 within the chamber 6 through the transportopening 66 by a transport robot located outside the apparatus. Thesemiconductor wafer W transported into the heat treatment space 65 bythe transport robot is moved to a position directly above the holder 7and stopped. Then, the pair of transfer arms 11 of the transfermechanism 10 are horizontally moved from the retracted position to thetransfer operation position and elevated, so that the lift pins 12 passthrough the through holes 79 and protrude from the upper surface of theholding plate 75 of the susceptor 74 to receive the semiconductor waferW. At this time, the lift pins 12 are elevated above the upper end ofthe substrate support pins 77.

After the semiconductor wafer W is placed on the lift pins 12, thetransport robot retracts from the heat treatment space 65, and thetransport opening 66 is closed with the gate valve 185. Then, the pairof transfer arms 11 are lowered so that the semiconductor wafer W istransferred from the transfer mechanism 10 to the susceptor 74 of theholder 7 and held in the horizontal position from below by the susceptor74. The semiconductor wafer W is supported by the plurality of substratesupport pins 77 provided upright on the holding plate 75 and is held onthe susceptor 74. The semiconductor wafer W is held by the holder 7 withthe front surface thereof, which has been patterned and implanted withimpurities, facing upward. A predetermined gap is formed between theback surface (the main surface on the side opposite to the frontsurface) of the semiconductor wafer W supported by the plurality ofsubstrate support pins 77 and the holding surface 75 a of the holdingplate 75. The pair of transfer arms 11 that have been lowered below thesusceptor 74 are retracted to the retracted position, or in other words,to the inside of the recessed portion 62, by the horizontal movementmechanism 13.

After the semiconductor wafer W is held in the horizontal position frombelow by the susceptor 74 of the holder 7, all the 40 halogen lamps HLof the halogen heater 4 turn on at once to start preheating(assist-heating). The halogen light emitted from the halogen lamps HLpasses through the lower chamber window 64 and the susceptor 74, whichare made of quartz, and is applied to the back surface of thesemiconductor wafer W. The semiconductor wafer W that has received thelight emitted from the halogen lamps HL is preheated, and thus thetemperature of the semiconductor wafer W increases. Here, the transferarms 11 of the transfer mechanism 10 will not impede the heating withthe halogen lamps HL because they have already been retracted into therecessed portion 62.

For preheating with the halogen lamps HL, the temperature of thesemiconductor wafer W is measured by the radiation thermometer 120. Morespecifically, the radiation thermometer 120 receives infrared lightradiated through the opening 78 from the back surface of thesemiconductor wafer W held by the susceptor 74, and measures theincreasing wafer temperature. The measured temperature of thesemiconductor wafer W is transmitted to the controller 3. The controller3 controls the output of the halogen lamps HL while monitoring whetherthe temperature of the semiconductor wafer W raised by the applicationof light from the halogen lamps HL has reached a predeterminedpreheating temperature T1. More specifically, the controller 3 performsfeedback control of output from the halogen lamps HL on the basis ofmeasurements by the radiation thermometer 120 so that the temperature ofthe semiconductor wafer W reaches the preheating temperature T1. Thepreheating temperature T1 is set to about 200° C. to 800° C. at whichthe impurities implanted in the semiconductor wafer W are not caused tobe diffused by heat, and preferably, may be set to about 350° C. to 600°C. (in the present embodiment, 600° C.).

After the temperature of the semiconductor wafer W reaches thepreheating temperature T1, the controller 3 temporarily maintains thesemiconductor wafer W at the preheating temperature T1. Specifically, atthe point in time when the temperature of the semiconductor wafer Wmeasured by the radiation thermometer 120 reaches the preheatingtemperature T1, the controller 3 controls the output of the halogenlamps HL to maintain the temperature of the semiconductor wafer Wapproximately at the preheating temperature T1.

This preheating with the halogen lamps HL allows the temperature of theentire semiconductor wafer W to uniformly increase to the preheatingtemperature T1. In the preheating stage with the halogen lamps HL, thetemperature of the peripheral portion of the semiconductor wafer W,where heat more easily dissipates, tends to drop lower than thetemperature of the central portion. On the other hand, the halogen lampsHL in the halogen heater 4 are arranged with higher density in theregion opposed to the peripheral portion of the semiconductor wafer Wthan in the region opposed to the central portion of the semiconductorwafer W. Accordingly, a larger amount of light is applied to theperipheral portion of the semiconductor wafer W where heat easilydissipates. In this condition, the in-plane temperature distribution ofthe semiconductor wafer W becomes uniform in the preheating stage.Moreover, the mirror-finished inner circumferential surface of thereflection ring 69 attached to the chamber side portion 61 increases theamount of light reflected by the inner circumferential surface of thereflection ring 69 toward the peripheral portion of the semiconductorwafer W. Accordingly, the in-plane temperature distribution of thesemiconductor wafer W becomes more uniform in the preheating stage.

After a lapse of a predetermined period from the time when thetemperature of the semiconductor wafer W has reached the preheatingtemperature T1 by the application of light emitted from the halogenlamps HL, flash light is applied from the flash lamps FL of the flashheater 5 to the front surface of the semiconductor wafer W. At thistime, part of the flash light radiated from the flash lamps FL travelsdirectly into the chamber 6, whereas another part of the flash light isreflected by the reflector 52 and then travels into the chamber 6. Theflash light is applied to the semiconductor wafer W for flash heating.

Flash heating is performed with the flash lamps FL emitting the flashlight, allowing for an increase in temperature of the front surface ofthe semiconductor wafer W in a short time. More specifically, the flashlight emitted from the flash lamps FL is extremely short intense flashlight that results from the conversion of the electrostatic energypreviously stored in the capacitor into an extremely short optical pulseand whose irradiation time is approximately longer than or equal to 0.1millisecond and shorter than or equal to 100 milliseconds. Thetemperature of the front surface of the semiconductor wafer W subjectedto flash heating with the flash lamps FL emitting the flash lightinstantaneously rises to a treatment temperature T2 of greater than orequal to 1000° C., and then rapidly drops after the activation of theimpurities implanted in the semiconductor wafer W. Since the temperatureof the front surface of the semiconductor wafer W can increase anddecrease in an extremely short time in the manner above, the heattreatment apparatus 1 can activate the impurities while suppressingthermal diffusion of the impurities implanted in the semiconductor waferW. Note that the time required for the activation of the impurities isextremely short as compared with the time required for the thermaldiffusion of the impurities, and thus the activation will be completedeven in such a short time of approximately 0.1 to 100 milliseconds thatcauses no diffusion.

After completion of the flash heat treatment and a lapse of apredetermined period of time, the halogen lamps HL turn off. Thetemperature of the semiconductor wafer W thus rapidly drops from thepreheating temperature T1. The decreasing temperature of thesemiconductor wafer W is measured by the radiation thermometer 120, andthe measurement result is transmitted to the controller 3. Thecontroller 3 monitors whether the temperature of the semiconductor waferW has dropped to a predetermined temperature on the basis of themeasurement result. After the temperature of the semiconductor wafer Whas dropped to the predetermined temperature or lower, the pair of thetransfer arms 11 of the transfer mechanism 10 are moved horizontallyagain from the retracted position to the transfer operation position andmoved upward, so that the lift pins 12 protrude from the upper surfaceof the susceptor 74 and receive the heat-treated semiconductor wafer Wfrom the susceptor 74. Then, the transport opening 66 closed by the gatevalve 185 is opened and the semiconductor wafer W placed on the liftpins 12 is transported by the transport robot located outside theapparatus. This completes the heat treatment of the semiconductor waferW in the heat treatment apparatus 1.

During the application of the flash light emitted from the flash lampsFL, the temperature of the front surface of the semiconductor wafer Winstantaneously increases to the treatment temperature T2 of greaterthan or equal to 1000° C., whereas the temperature of the back surfaceof the semiconductor wafer W at that time does not increase so much fromthe preheating temperature T1. In other words, a difference intemperature instantaneously occurs between the front and back surfacesof the semiconductor wafer W. As a result, abrupt thermal expansionoccurs only in the front surface of the semiconductor wafer W, whereasthe back surface hardly undergoes thermal expansion. Thus, thesemiconductor wafer W instantaneously warps such that the front surfacethereof becomes raised.

FIG. 8 is a schematic view showing how the semiconductor wafer W warpsduring the application of the flash light. The application of the flashlight abruptly increases the temperature of only the front surface ofthe semiconductor wafer W in which thermal expansion occurs. Thus, thesemiconductor wafer W warps such that the front surface thereof becomesraised. As a result, the lower surface of the semiconductor wafer W isinevitably bent inward. At this time, compressive stress is exerted onthe vicinity of the central portion of the lower surface of thesemiconductor wafer W as indicated with arrows AR 81 while tensilestress is exerted on the peripheral portion of the lower surface asindicated with arrows AR 82. In other words, stress is exerted on thevicinity of the central portion and the peripheral portion of the lowersurface of the semiconductor wafer W in opposite directions (tensiledirection and compressive direction) during the application of the flashlight. This indicates the presence of a portion on which no stress isexerted in the lower surface of the semiconductor wafer W during theapplication of the flash light. The portion serves as a boundary betweenthe region on which compressive stress is exerted and the region onwhich tensile stress is exerted in the lower surface of thesemiconductor wafer W.

FIG. 9 shows a transition of a position on which no stress is exerted inthe lower surface of the semiconductor wafer W during the application ofthe flash light. FIG. 9 shows the transition of the position on which nostress is exerted in the lower surface of the semiconductor wafer Whaving a diameter of 300 mm when the flash light is applied to the uppersurface thereof. In FIG. 9 , the horizontal axis indicates elapsed timesince the start of the application of the flash light emitted from theflash lamps FL, and the vertical axis indicates a distance (diameter)from the center of the lower surface of the semiconductor wafer W.

As shown in FIG. 9 , the position on which no stress is exerted varieswith the elapsed time since the start of the application of the flashlight, the position serving as the boundary between the region on whichcompressive stress is exerted and the region on which tensile stress isexerted in the lower surface of the semiconductor wafer W. When theelapsed time since the start of the application of the flash light ist1, the upper surface of the semiconductor wafer W reaches the maximumtemperature (above-mentioned treatment temperature T2), and the greatestbending stress is exerted on the semiconductor wafer W. When the elapsedtime since the start of the application of the flash light is t1 (thatis to say, when the upper surface of the semiconductor wafer W reachesthe maximum temperature), the position on which no stress is exerted inthe lower surface of the semiconductor wafer W is located farthest fromthe center, and a distance at that time from the center to the positionon which no stress is exerted is 135 mm.

FIG. 10 shows a stress distribution of the lower surface of thesemiconductor wafer W during the application of the flash light. FIG. 10shows the stress distribution of the lower surface of the semiconductorwafer W at the moment when the upper surface of the semiconductor waferW having the diameter of 300 mm reaches the maximum temperature by beingirradiated with the flash light (that is to say, at the moment when theelapsed time since the start of the application of the flash light ist1). In FIG. 10 , the horizontal axis indicates a distance from thecenter of the lower surface of the semiconductor wafer W, and thevertical axis indicates stress.

When the upper surface of the semiconductor wafer W reaches the maximumtemperature after time t1 has elapsed since the start of the applicationof the flash light emitted from the flash lamps FL to the upper surface,compressive stress is exerted on the central region at a distance ofless than 135 mm from the center of the lower surface of thesemiconductor wafer W, and tensile stress is exerted on the peripheralregion at a distance of greater than 135 mm from the center thereof. Nostress is exerted in the position at a distance of 135 mm from thecenter of the lower surface of the semiconductor wafer W, the positionserving as the boundary between the central region on which compressivestress is exerted and the peripheral region on which tensile stress isexerted.

In the present embodiment, the 12 substrate support pins 77 are providedon the susceptor 74 so as to contact the position in the lower surfaceat the distance of 135 mm from the center of the semiconductor wafer Wand on which no stress is exerted at the moment when the upper surfaceof the semiconductor wafer W reaches the maximum temperature during theapplication of the flash light. Specifically, the 12 substrate supportpins 77 are provided upright every 30 degrees on the holding surface 75a of the holding plate 75 along the circumference of the circle that isconcentric with the outer circumferential circle of the semiconductorwafer W and that has the diameter of 270 mm (the circle indicated by thebroken line in FIG. 3 ). The 12 substrate support pins 77 contact thecircle that is concentric with the outer circumferential circle of thesemiconductor wafer W and that has the diameter of 270 mm on the lowersurface of the semiconductor wafer W.

During the application of the flash light, when the substrate supportpins 77 contact a position on which stress is exerted in the lowersurface of the semiconductor wafer W, that is to say, when the substratesupport pins 77 contact the central region on which compressive stressis exerted and at the distance of less than 135 mm from the center orthe peripheral region on which tensile stress is exerted and at thedistance of greater than 135 mm from the center, stress concentrationoccurs in the contact position of the semiconductor wafer W thatcontacts the substrate support pins 77, causing the semiconductor waferW to break.

In the present embodiment, when the upper surface of the semiconductorwafer W is irradiated with the flash light emitted from the flash lampsFL and thus reaches the maximum temperature, the plurality of substratesupport pins 77 contact the position on which no stress is exerted inthe lower surface of the semiconductor wafer W. Thus, stressconcentration does not occur in the contact position of the lowersurface of the semiconductor wafer W that contacts the plurality ofsubstrate support pins 77. This can prevent the semiconductor wafer Wfrom breaking during the application of the flash light emitted from theflash lamps FL.

While the preferred embodiment of the present invention has beendescribed above, various modifications in addition to those describedabove may be made to the invention without departing from the purpose ofthe invention. For example, the semiconductor wafer W having thediameter of 300 mm has been described in the preferred embodiment above,but the present invention is not limited thereto. The semiconductorwafer W may have a diameter of 450 mm, for example. For thesemiconductor wafer W having the diameter of 450 mm, the position onwhich no stress is exerted in the lower surface at the moment when theupper surface of the semiconductor wafer W reaches the maximumtemperature during the application of the flash light is located at adistance of 405 mm from the center of the lower surface of thesemiconductor wafer W. Thus, the plurality of substrate support pins 77are provided so as to contact the circle that is concentric with theouter circumferential circle of the semiconductor wafer W having thediameter of 450 mm and that has the diameter of 405 mm on the lowersurface of the semiconductor wafer W. In this manner, similarly to thepreferred embodiment above, when the upper surface of the semiconductorwafer W reaches the maximum temperature during the application of theflash light, the plurality of substrate support pins 77 contact theposition on which no stress is exerted in the lower surface of thesemiconductor wafer W, and thus stress concentration does not occur inthe contact position of the semiconductor wafer W that contacts thesubstrate support pins 77. This can prevent the semiconductor wafer Wfrom breaking during the application of the flash light.

The semiconductor wafer W may have a diameter other than 300 mm and 450mm. To summarize, it is sufficient as long as the plurality of substratesupport pins 77 are provided so as to contact the position on which nostress is exerted in the lower surface of the semiconductor wafer W whenthe upper surface of the semiconductor wafer W is irradiated with theflash light emitted from the flash lamps FL and thus reaches the maximumtemperature. The position on which no stress is exerted in the lowersurface at the moment when the upper surface of the semiconductor waferW reaches the maximum temperature during the application of the flashlight is located on a circle that is concentric with the outercircumferential circle of the semiconductor wafer W and that has adiameter of 90% of the diameter of the semiconductor wafer W. In otherwords, it is sufficient as long as the plurality of substrate supportpins 77 are provided so as to contact the circle that is concentric withthe outer circumference circle of the semiconductor wafer W and that hasthe diameter of 90% of the diameter of the semiconductor wafer W. Inthis manner, stress concentration does not occur in the contact positionof the semiconductor wafer W that contacts the substrate support pins77, which can prevent the semiconductor wafer W from breaking during theapplication of the flash light.

Although the flash heater 5 includes the 30 flash lamps FL in thepreferred embodiment above, the present invention is not limitedthereto. The flash heater 5 may include a freely-selected number offlash lamps FL. The flash lamps FL are not limited to xenon flash lamps,and may be krypton flash lamps. The number of halogen lamps HL includedin the halogen heater 4 is not limited to 40 and may be freely selected.

Although the semiconductor wafer W is preheated by the application ofthe halogen light from the halogen lamps HL in the preferred embodimentabove, a preheating technique is not limited to this technique. Thesemiconductor wafer W may be placed on a hot plate and be preheatedinstead. Even in this case, the same arrangement of the plurality ofsubstrate support pins 77 on the susceptor located on the hot plate asthe arrangement in the preferred embodiment above can prevent thesemiconductor wafer W from breaking during the application of the flashlight.

A substrate to be treated by the heat treatment apparatus of the presentinvention is not limited to a semiconductor wafer, and may be a glasssubstrate used in a flat-panel display such as a liquid crystal display,or a substrate for use in solar cell. The technology of the presentinvention is also applicable to heat treatment of a high dielectric gateinsulating film (high-k film), bonding between metal and silicon,crystallization of polysilicon, or the like.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It istherefore understood that numerous other modifications and variationscan be devised without departing from the scope of the invention.

What is claimed is:
 1. A heat treatment method for irradiating a substrate having a center with flash light emitted from a flash lamp to heat the substrate, comprising the steps of: (a) placing a substrate at upper ends of a plurality of support pins that are provided upright on a holding plate having a planar holding surface to hold the substrate; and (b) irradiating an upper surface of the substrate with flash light, whose irradiation time is longer than or equal to 0.1 millisecond and shorter than or equal to 100 milliseconds, emitted from the flash lamp, in a manner so that a lower surface of the substrate becomes subjected to a compressive stress at a central region thereof and to a tensile stress outside the central region when the upper surface of the substrate reaches a maximum temperature, with a boundary therebetween at which no stress is exerted on the lower surface, wherein in the step (a), the substrate is placed on the plurality of support pins so that the plurality of support pins contact the lower surface of the substrate only at the boundary at which no stress is exerted on the lower surface of the substrate when the upper surface of the substrate reaches the maximum temperature in the step (b), said boundary where no stress is exerted on the lower surface of said substrate being located at a given distance from said center of said substrate.
 2. The heat treatment method according to claim 1, wherein the substrate has a circular plate shape, and in the step (a), the plurality of support pins contacts a circle that is concentric with an outer circumferential circle of the substrate and has a diameter of 90% of the diameter of the substrate.
 3. The heat treatment method according to claim 2, wherein the plurality of support pins comprise 12 support pins located every 30 degrees along the circumference of the concentric circle. 